Two large scientific studies have found seven new genetic variants that make people put on weight, to add to two genes that were already linked to obesity in the general population. Both research teams - one led by deCode Genetics, an Icelandic biotechnology company, and the other an international academic consortium - published their findings yesterday in the journal Nature Genetics. The discoveries will be important for the global fight against obesity, one of the greatest public health problems of the 21st century.
The most significant feature of the newly identified genes is that almost all of them are active in the brain, implying that they affect appetite rather than the biochemical processes of energy or fat metabolism. "This suggests that, as we work to develop better means of combating obesity, including using these discoveries as the first step in developing new drugs, we need to focus on the regulation of appetite at least as much as on the metabolic factors of how the body uses and stores energy," said Kari Stefansson, chief executive of deCode. Samples from a total of more than 100,000 people were analysed in the two "genome-wide association studies", which used the latest DNA-reading technology to associate genetic variations with body mass index.
Body mass index is the most commonly used measure of obesity.
Family and twin studies have shown that genetic factors account for 40-70 per cent of population variation in body mass index. Yet the first gene contributing to obesity in the general population, as opposed to people with rare metabolic disorders, was not discovered until 2007. Each of the newly identified genetic variations has only a modest effect: someone who carries all seven would typically be 1.5kg to 2kg heavier than an average adult.
That meant that dozens, or even hundreds, more genetic variations probably contributed small amounts to obesity, said Joel Hirschhorn, of Children's Hospital Boston, who led the academic consortium. Mark McCarthy, of Oxford University, another member of the consortium, said: "It may seem surprising that we know so little about the biology of such an important medical and social issue.
"We are finding that common diseases have complex causes and it is only by understanding the biology that we can start to make rational attempts to treat and prevent conditions such as obesity," he added.